The present invention relates generally to safety systems to protect persons from injury from industrial machines, and more particularly, to a system for terminating power and indicating an active condition of a machine.
It is known in the art to provide safety systems for dangerous machinery and industrial apparatus to protect persons from injury from such equipment. Such dangerous equipment includes welding machines, robotic assembly devices, metal cutting equipment and the like, all of which may be self-operating or person-operated. Generally, safety systems for such machinery typically involve some form of means for preventing personnel from inadvertently approaching the dangerous equipment or involve some form of alarm or power cut-off to the machine which is activated upon a dangerous condition, such as when a person gets too close to the dangerous equipment. Examples of such safety systems include dual hand operated controls which forces an operator to keep both hands on the controls, presence sensing devices incorporating light beams and receivers and electric switch mats connected to a machine controller for terminating power to the machine if someone steps on or off the mat.
Various types of electrical switch mats are known in the art. Electrical switch mats have been designed for use in many different applications including use in floor mats for security, safety or other purposes to detect movement of objects or pedestrian traffic thereover. Generally, electrical switch mats include one or more pressure-actuated switches incorporated within a floor mat material which protects the switch against wear. For example, normally open and normally closed pressure-sensitive electrical ribbon switches have been incorporated into numerous designs for electrical switch mats. Open and closed pressure-sensitive ribbon switches generally include a pair of either spaced or closed conductors respectively supported in an insulative jacket. Generally, relatively light pressure on the jacket will close the space in an open switch and open the conductors in a close switch thereby activating the switch. Thus, someone stepping on or off an electrical switch mat having a ribbon switch incorporated therein will activate the switch.
Electrical switch mats as described above have been extremely useful in detecting and responding to the presence, or absence, of the operator or others anywhere on its sensing surface, wherein the sensing surface is defined as the area covered by a single mat or a plurality of mats in combination. In one typical application, one or more sensing mats are placed directly in front of a piece of machinery, wherein the machine operator stands on the mat during operation of the machinery. If the operator steps off the mat, or if someone else steps on the mat, the switch mat is activated to terminate power to the machine.
In another application, the dangerous equipment may be surrounded by a plurality of switch mats to define a danger zone, wherein a person entering the danger zone will step on a mat, thereby activating a switch to terminate power to the equipment. Alternatively, the dangerous equipment may be substantially surrounded by a protective barrier, such as a guard cage or fence, to define a danger zone and a switch mat is placed at the only entrance into the danger zone. Similarly, anyone entering the danger zone will step on the switch mat to terminate power to the dangerous equipment.
While such switch mat based safety systems are effective in terminating power to a piece of dangerous equipment upon a change in status within the danger zone, it is often difficult for persons approaching such a danger zone to ascertain the present status within the danger zone. In particular, a person having a need to enter the danger zone may not be able to easily determine if it is indeed safe to enter (e.g., the dangerous machinery is already turned off), or whether the zone is in a danger status (e.g. the machinery is operating).
Accordingly, it would be desirable to provide a machine guarding safety system that can readily indicate a present status of a danger zone surrounding the dangerous machinery. It would be further desirable to provide a machine guarding safety system utilizing a switch mat having a visual status indicator incorporated directly in the switch mat to display an active status of the danger zone to those approaching the switch mat.